I've done a lot of projects over the holidays. This is a quick collection of notes to remind myself later.

I used an RC522 RFID scanner (originally part of a Tonuino project) and wired it to a Particle Photon. Whenever an RFID tag was held to it, it would publish an event containing the ID of the card to the Particle Cloud. When the card was removed, it would publish a blank event. This is the code from the Photon:

// Photon   RFID-RC522
//   A2         SDA
//   A3         SCK
//   A4         MISO
//   A5         MOSI
//   D2         RST
//   GND        GND
//   3V3        3.3V


#define LED_PIN     D7

constexpr uint8_t RST_PIN = D2;          // Configurable, see typical pin layout above
constexpr uint8_t SS_PIN =  A2;           // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN);  // Create MFRC522 instance

uint32_t lastMillis = 0;
bool wasPresent = false;

void setup() {
    pinMode(LED_PIN, OUTPUT);
	Serial.begin(9600);		// Initialize serial communications with the PC
	while (!Serial);		// Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
	SPI.begin();			// Init SPI bus
	mfrc522.PCD_Init();		// Init MFRC522
	mfrc522.PCD_DumpVersionToSerial();	// Show details of PCD - MFRC522 Card Reader details
	Serial.println(F("Scan PICC to see UID, SAK, type, and data blocks..."));

void loop() {
	// Look for new cards
	if ( ! mfrc522.PICC_IsNewCardPresent()) {
	    if(wasPresent) {
	        if(! mfrc522.PICC_IsNewCardPresent()) {
	          Serial.println("No card");
	          Particle.publish("rfid_scan", "", 60, PRIVATE);
	          wasPresent = false;
	    } else {

	// Select one of the cards
	if ( ! mfrc522.PICC_ReadCardSerial()) {

    char cardID[32] = "";

    for (byte i = 0; i < mfrc522.uid.size; i++) {
     char hex[4];
     snprintf(hex, sizeof(hex), "%02x", mfrc522.uid.uidByte[i]);
     strncat(cardID, hex, sizeof(cardID));

    if (millis() - lastMillis < 1000) {
    lastMillis = millis();

	if(!wasPresent) {
	    wasPresent = true;
	    Particle.publish("rfid_scan", cardID, 60, PRIVATE);
	    Serial.printlnf("Card: %s", cardID);

	    // Turn on the LED
	    digitalWrite(LED_PIN, HIGH);

	    // Leave it on for one second

	    // Turn it off
	    digitalWrite(LED_PIN, LOW);

	    // Wait one more second

	// Dump debug info about the card; PICC_HaltA() is automatically called

I then used IFTTT to read these events and write them to a Google Spreadsheet. This is the IFTTT Excel code:

{{CreatedAt}} |||{{EventContents}}||| =IF(ISODD(ROW()), "Started", "Stopped") ||| =IF(ISEVEN(ROW()),ROUND(((DATEVALUE(REGEXEXTRACT(INDIRECT(ADDRESS(ROW(),COLUMN()-3,4)), "w+ d{2}, d{4}")) + TIMEVALUE(REGEXEXTRACT(INDIRECT(ADDRESS(ROW(),COLUMN()-3,4)), "d{2}:d{2}[A|P]M$"))) - ( DATEVALUE(REGEXEXTRACT(INDIRECT(ADDRESS(ROW()-1,COLUMN()-3,4)), "w+ d{2}, d{4}")) + TIMEVALUE(REGEXEXTRACT(INDIRECT(ADDRESS(ROW()-1,COLUMN()-3,4)), "d{2}:d{2}[A|P]M$")))) * 24, 2),"")|||

We now have a physical time tracker that can be used to log time spent on individual projects. Super-handy for Jenni's freelance work.